The present invention relates to a tension tester which measures tensile characteristics of material by using a scanning device such as a television camera, a line sensor camera and a laser scanner camera.
In a tension tester which measures tensile characteristics such as tensile strength, tensile stress and elongation at fracture of materials such as rubber, resin and fiber, a test piece of these materials is held by chucks at the ends and one chuck is pulled to apply a tensile load to the test piece and produce an elongation deformation. With such a tension tester, the process of measuring the tensile stress at, say, 100% elongation requires an inspector to watch the test piece being stretched and determine the point at which the elongation has just reached 100%. This process requires a high level of skill on the part of the inspector, and an unskilled inspector may often produce errors in measurements.
To eliminate the problem of measurement errors which occur depending on the level of skill of the experimenting staff, the inventors of this invention have already proposed tension testers in the Japanese Patent Publications No. 56-19882 and No. 56-18086 in which the test piece is marked with lines which have different optical characteristics from those of the test piece and which are automatically measured by a television camera (hereafter simply referred to as TV camera).
With materials such as rubber which are greatly elongated to 5 to 10 times the original length before being broken, it may sometimes be necessary to investigate the elongation characteristic in a small deformation range as well as in a large deformation range. However, the measurement of tension characteristic during the minute deformation demands higher skills, and the tension tester cited above using a TV camera is appropriate for such measurement. The above-mentioned conventional tension tester using the TV camera, however, has the following disadvantage. That is, when the minute change is measured by putting the camera close to the test piece, the large deformation goes out of sight of the TV camera and cannot be measured. In other words, the conventional testing device cannot take measurement of both minute deformations and large deformations at the same time with a single measurement setting. This lowers the efficiency of experiments. A same as this can also be said of other devices using line sensor camera or laser scanner camera instead of TV camera.